convolution.c

#include <stdio.h>
#include <TMath.h>
#include <TCanvas.h>
#include <iostream>
#include <TROOT.h>
#include <TChain.h>
#include <TObject.h>
#include <TRandom.h>
#include <TFile.h>
#include <math.h>
#include <TF1Convolution.h>
#include <TF1.h>
#include <TH1F.h>
#include <TGraph.h>
#include <TStopwatch.h>


using namespace std;


void fitConvolution()
{

   //tutorial for convolution of two functions
   
   
   //construction of histogram to fit
   TH1F *h_ExpGauss = new TH1F("h_ExpGauss","Exponential convoluted by gaussian",100,0.,5.);
   for (int i=0;i<1e6;i++)
   {
      Double_t x = gRandom->Exp(1./0.3);//gives a alpha of -0.3 in the exp
      x += gRandom->Gaus(0.,3.);
      h_ExpGauss->Fill(x);//probability density function of the addition of two variables is the convolution of 2 dens. functions
   }

   TF1Convolution *f_conv = new TF1Convolution("expo","gaus",-1,6,true);
   f_conv->SetRange(-1.,6.);
   f_conv->SetNofPointsFFT(1000);
   TF1   *f = new TF1("f",*f_conv, 0., 5., f_conv->GetNpar());
   f->SetParameters(1.,-0.3,0.,1.);
   
   //fit
   new TCanvas("c","c",800,1000);
   h_ExpGauss -> Fit("f");
   h_ExpGauss->Draw();
  
}